Traveling wave quantum well waveguide modulators using velocity matching for improved frequency performance

Abstract

An optoelectronic modulator modulates an optical signal in response to an electromagnetic signal. The optoelectronic modulator includes a waveguide for conveying the optical signal, where the waveguide has an associated width, core thickness, and waveguide-electrode separation, and includes a optical index of refraction with respect to the optical signal and a microwave index of refraction with respect to the electromagnetic signal; and where the microwave index of refraction substantially matches the optical index of refraction for velocity-matching the optical signal and the electromagnetic signal through the waveguide. The waveguide may be disposed on an n-type doped substrate, may include a quantum well region disposed on the substrate, and may have a predetermined width for providing the matching of refractive indices.

What is claimed is: 
     
       1. An optoelectronic modulator for modulating an optical signal in response to an electromagnetic signal, the optoelectronic modulator comprising: a waveguide for receiving the optical signal, wherein the waveguide has an associated width and includes:   an optical index of refraction with respect to the optical signal; and   a microwave index of refraction with respect to the electromagnetic signal;   wherein the waveguide is fabricated with the microwave index of refraction substantially matching the optical index of refraction for velocity-matching the optical signal and the electromagnetic signal through the waveguide and for providing a frequency bandwidth in excess of about 40 GHz.   
     
     
       2. The optoelectronic modulator of claim 1 further comprising: a substrate; and   a lower cladding layer disposed upon the substrate;   wherein the waveguide further includes: an upper cladding layer; and   a quantum well region positioned between the upper and lower cladding layers.     
     
     
       3. The optoelectronic modulator of claim 2 wherein the quantum well region includes a plurality of Barrier Reservoir and Quantum Well Electron Transfer (BRAQWET) structures. 
     
     
       4. The optoelectronic modulator of claim 2 wherein the electromagnetic signal is applied between the upper cladding layer and the substrate to modulate the optical signals. 
     
     
       5. The optoelectronic modulator of claim 2 wherein the substrate has an n-type doped composition. 
     
     
       6. The optoelectronic modulator of claim 2 wherein the substrate includes a semi-insulating composition. 
     
     
       7. The optoelectronic modulator of claim 1 wherein the waveguide is configured as a substantially straight rib having an associated width, core thickness, and waveguide-electrode separation which determine the matching of optical and microwave indices of refraction. 
     
     
       8. The optoelectronic modulator of claim 7 further comprising a doped substrate; wherein the optical index of refraction is about 3.3;   the associated width is within the range of 2.5 μm and 3.9 μm;   the waveguide-electrode separation is within the range of 7 μm and 15 μm; and   the core thickness is within the range of 0.5 μm and 0.8 μm, to determine the microwave index of refraction to be about 4.0.   
     
     
       9. The optoelectronic modulator of claim 1 further comprising a semi-insulating substrate; wherein the optical index of refraction is about 3.3, and the microwave index of refraction is about 3.3.   
     
     
       10. An optoelectronic modulator for modulating an optical signal in response to an electromagnetic signal, the optoelectronic modulator comprising: a substrate;   a contact pad for receiving the electromagnetic signal; and   a waveguide operatively connected to the substrate and to the contact pad, and including a rib for receiving the optical signal and having: an optical index of refraction with respect to the optical signal; and   a microwave index of refraction with respect to the electromagnetic signal;   wherein the microwave index of refraction substantially matches the optical index of refraction for velocity-matching the optical signal and the electromagnetic signal through the waveguide for modulating the optical signal, and for providing a bandwidth associated with the optoelectronic modulator of about 40 GHz at about 3 dB.     
     
     
       11. The optoelectronic modulator of claim 10 wherein the waveguide includes a quantum well region. 
     
     
       12. The optoelectronic modulator of claim 11 wherein the quantum well region includes a plurality of Barrier Reservoir and Quantum Well Electron Transfer (BRAQWET) structures. 
     
     
       13. The optoelectronic modulator of claim 11 wherein the quantum well region is disposed between the substrate and the contact pad for receiving the electromagnetic signal applied between the substrate and the contact pad to modulate the optical signals. 
     
     
       14. The optoelectronic modulator of claim 10 wherein the substrate has an n-type InP:Si composition. 
     
     
       15. The optoelectronic modulator of claim 10 wherein the substrate is an n-type doped substrate and the waveguide is configured as a rib having an associated width, core thickness, and waveguide-electrode separation which determine the matching of optical and microwave indices of refraction. 
     
     
       16. The optoelectronic modulator of claim 15 wherein the optical index of refraction is about 3.3; and the associated width is within the range of 2.5 μm and 3.9 μm to determine the microwave index of refraction to be about 4.0.   
     
     
       17. The optoelectronic modulator of claim 10 wherein the substrate is a semi-insulating substrate; and the waveguide is configured such that the optical index of refraction is about 3.3, and the microwave index of refraction to be about 4.0.   
     
     
       18. An optoelectronic modulator for modulating an optical signal in response to an electromagnetic signal, the optoelectronic modulator comprising: a substrate having an n-type doped composition;   a lower cladding layer positioned upon the substrate; and   a waveguide having a rib with an associated width in a coplanar-microstrip configuration for receiving the optical signal and operatively connected to the substrate through the lower cladding layer, having: a quantum well region;   an optical index of refraction with respect to the optical signal; and   a microwave index of refraction with respect to the electromagnetic signal;   wherein the microwave index of refraction substantially matches the optical index of refraction for velocity-matching the optical signal and the electromagnetic signal through the waveguide, for modulating the optical signal, and for providing a bandwidth associated with the optoelectronic modulator of about 40 GHz at about 3 dB.     
     
     
       19. The optoelectronic modulator of claim 18 wherein the width is about 2.5 μm for substantially matching the optical and microwave indices of refraction. 
     
     
       20. The optoelectronic modulator of claim 18 wherein the rib of the waveguide is substantially straight and positioned upon the lower cladding layer, with the rib including: the quantum well region; and   an upper cladding layer for receiving the electromagnetic signal from an electrode.   
     
     
       21. The optoelectronic modulator of claim 20 wherein the electromagnetic signal is applied between the upper cladding layer and the substrate to modulate the optical signals. 
     
     
       22. The optoelectronic modulator of claim 18 wherein quantum well region includes a plurality of Barrier Reservoir and Quantum Well Electron Transfer (BRAQWET) periods, with each period including: an InGaAlAs reservoir being Si-doped and having a bandgap of about 1.06 eV bandgap;   an undoped InGaAlAs spacer;   an InGaAs quantum well; and   an InAlAs barrier.   
     
     
       23. The optoelectronic modulator of claim 2 wherein the quantum well region includes a heterostructure. 
     
     
       24. The optoelectronic modulator of claim 23 wherein the quantum well region includes alternating layers of InGaAsP quantum wells as the heterostructure. 
     
     
       25. The optoelectronic modulator of claim 1 wherein the waveguide is configured as at least a portion of a second waveguide structure having the matching of optical and microwave indices of refraction. 
     
     
       26. The optoelectronic modulator of claim 25 wherein the second waveguide structure is a directional coupler. 
     
     
       27. The optoelectronic modulator of claim 25 wherein the second waveguide structure is a Y-branch switch. 
     
     
       28. The optoelectronic modulator of claim 25 wherein the second waveguide structure is a modulator structure. 
     
     
       29. The optoelectronic modulator of claim 28 wherein the second waveguide structure is an optical intensity modulator. 
     
     
       30. The optoelectronic modulator of claim 28 wherein the second waveguide structure is an interferometer structure. 
     
     
       31. An optoelectronic modulator for modulating an optical signal in response to an electromagnetic signal, the optoelectronic modulator comprising: a waveguide for receiving the optical signal, wherein the waveguide has an associated width and includes: an optical index of refraction of about 3.3 with respect to the optical signal; and     a microwave index of refraction with respect to the electromagnetic signal;   wherein the waveguide is fabricated with the microwave index of refraction substantially matching the optical index of refraction for velocity-matching the optical signal and the electromagnetic signal through the waveguide, wherein the waveguide is configured as a substantially straight rib having an associated width within the range of 2.5 μm and 3.9 μm, a core thickness within the range of 0.5 μm and 0.8 μm, and a waveguide-electrode separation within the range of 7 μm and 15 μm which determine the matching of optical and microwave indices of refraction with the microwave index of refraction being about 4.0.